OBJECTIVES: To assess strength and duration of pelvic floor muscle (PFM) contraction and to monitor the changes of lifestyle-related factors (body weight, constipation, vaginal wall laxity and physical activity) during pregnancy. METHODS: Our study focused on examining the strength and duration of pelvic floor muscle contraction in pregnant women during the 2nd and 3rd trimesters. Parameters were measured by a device for measuring vaginal pressure. Statistical data were calculated according to mean, standard deviation, T-test methods and  the results were considered to be relevant at p<0.05. RESULTS: Data of 93 women were analyzed. The maximum muscle strength of nulliparous women (n=36) was significantly higher (p=0.003) than that of pregnant women (n=57). The duration of maximum contraction in case of nulliparous women proved to be markedly longer (p=0.011) than during pregnancy. Regarding lifestyle factors even when BMI and constipation were involved no significant results were found in the two groups. Significantly lower muscle strength was observed in case of nulliparous women (n=18) who have experienced vaginal wall laxity (p=0.004) and in pregnant women. (p=0.0008) Duration of PFM contraction was significantly worse in pregnant women (p=0.001). Women who occasionally do some forms of physical activity showed a significantly better muscle strength (p=0.029), and women who regularly do some physical exercise showed a significantly longer duration of maximum contraction (p=0.018) than pregnant women doing occasional or regular exercise. Comparing only the results of pregnant women we found a significant difference in PFM strength of women doing occasional and regular exercise and almost significant results were found in women who never or occasionally do exercises. CONCLUSIONS: A significantly decreased maximum pelvic floor muscle strength and duration of maximum contraction could be observed in pregnancy compared to nulliparous young women doing regular or occasional physical exercise and experiencing vaginal wall laxity.